Open Redirect in reflex-dev/reflex

Summary

Reflex is a library to build full-stack web apps in pure Python. In versions 0.5.4 through 0.8.14, the /auth-codespace endpoint automatically assigns the redirect_to query parameter value directly to client-side links without any validation and triggers automatic clicks when the page loads in a GitHub Codespaces environment. This allows attackers to redirect users to arbitrary external URLs. The vulnerable route is only registered when a Codespaces environment is detected, and the detection is controlled by environment variables. The same behavior can be activated in production if the GITHUB_CODESPACES_PORT_FORWARDING_DOMAIN environment variable is set. The vulnerability occurs because the code assigns the redirect_to query parameter directly to a.href without any validation and immediately triggers a click (automatic navigation), allowing users to be sent to arbitrary external domains. The execution condition is based on the presence of a sessionStorage flag, meaning it triggers immediately on first visits or in incognito/private browsing windows, with no server-side origin/scheme whitelist or internal path enforcement defenses in place. This issue has been patched in version 0.8.15. As a workaround, users can ensure that GITHUB_CODESPACES_PORT_FORWARDING_DOMAIN is not set in a production environment.

Timeline

1. Oct 15, 2025, 3:57 PM UTCCVE published
2. Oct 15, 2025, 5:17 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Oct 15, 2025, 5:18 PM UTCRecord last updated

Affected versions

• reflex-dev reflex

  From 0.5.4 · fixed in 0.8.15

• reflexPyPI

  From 0.5.4 · through 0.8.14

References 2